Walking on water: pond skating in the summer

The spring emergence of insects is now well under way, benign and pesky alike. One of the more fascinating critters that are now visible is the pond skater, a member if the Gerridae family, which comprise several surface-dwelling insect species.

Pond skaters have a wax-like substance on their bodies that is hydrophobic, or repels water. This aids them in keeping above the surface of the water and also prevents them from drowning due to a water film covering the spiracles (orifices used for respiration) on their body. More significant in surface-dwelling ability is the phenomenon of surface tension of water.

Water molecules in a body of water are attracted to each other due to hydrogen bond charges and resulting re-alignment with neighboring water molecules. However, at the water’s surface, there is no bond interaction above the air-water interface. This causes the hydrogen bonds at the surface to be in a single direction, and this causes surface tension.

A pond skater weighs in at about 20 mg for a large individual and uses a portion of its legs for support on the surface. Based on its mass and surface area in contact with the water, it is estimated that it has only one seventh of the mass required to break through the surface film. An average person would have to have feet 1.5 miles long to mimic this feat.

Other species are also surface dwellers. To see an arachnid that can walk on water, visit www.riverreport[2] er.com/issues/08-10-23/rivertalk.html.